Abrasive blasting system



July 1956 R. R. GARVER ABRASIVE BLASTING SYSTEM 3 Sheets-Sheet 1 Filed April 20. 1953 mm hm mm mmm mm m N m an om um S m 3 INVENTOR. RALPH R. GARVER I ow w July 10. 1956 v I5 SheetsSheet 2 Filed April 20, 1953 INVENTOR. RALPH R. GARVER y 10, 1956 R. R. GARVER ABRASIVE BLASTING SYSTEM 3 Sheets-Sheet 3 Filed April 20, 1953 s T: 5 3 m V 4 m 0 6 m A m a s 1 1 n u m I j .1 H m a2 Y N l 6 8 TI 6 m H Hu 2% 2 4 m ,r w W l W 4 1; o T. M5 ,1 F 5 m INVENTOR. RALPH R. GARVER ABRASIVE BLASTLNG SYSTEM Ralph R. Garver, Hagerstown, Md., assignor to Pangborn Corporation, Hagerstown, Md., a corporation of Maryland Application April 20, 1953, Serial No. 349,643

Claims. (Cl. 51-8) This invention relates to an improved system for blasting various materials with a stream of abrasive particles to clean and/or surface treat the same. More particularly, the invention relates to an improved sandblasting apparatus including a manually portable abrasive gun and having a control system of novel construction and operation.

It has long been a vexatious problem in the abrasive blasting of work articles to provide reliable control arrangement for the turning on and off of the blasting by an operator who is manually holding and directing the discharge or nozzle end of a conduit through which the abrasive particles are impelled. This conduit discharge is generally some distance from the apparatus that impels the blastant into the conduit so that the operator cannot readily control the apparatus directly. Furthermore, practical consideration may require that such blasting be conducted in closed chambers, with the operator within the chamber, and actually out of reach of the impelling apparatus. Attempts have been made to use an electric switch inserted near the discharge nozzle and connected in circuit with a remote feed control valve. This arrangement has been found to require too much maintenance, the switch contact elements and mechanism rapidly becoming fouled with the finely divided'particles that are generated in large quantities by the blasting.

A principal object of the present invention is the avoidance of the above and related difficulties. A further object of the invention is to provide an automatic self-cleaning control mechanism for effecting remote energization of the blasting system from the blastant directing gun or nozzle. Other objects will become apparent from the description and claims which follow.

These objects are attained by providing a control structure near the blasting nozzle with a manually operative valve arrangement connected in a pressurized line to cause predetermined pressure changes in the line and thereby energize or deenergize the blastant stream. The control mechanism can be in the form of'a dead man control whereby when the directing nozzle or gun of the blastant supply line is manually gripped in a conventional manner, the manually operable valve mechanism is automatically actuated to cause the blastant stream to flow; but when the operator releases the nozzle or removes his hands therefrom, this valve is released and automatically deenergizes the blastant supply stream.

Having broadly described the invention, reference will now be made to a specific embodiment thereof which will be more fully understood by referring to the following specification, claims and drawings, and in which:

Fig. 1 is a schematic view, partly in section, of the blastant apparatus according to the present invention,

Fig. 2 is an enlarged cross-sectional view of the remote control mechanism of the Fig. 1 construction,

Fig. 3 illustrates the control circuit for the apparatus, and

Fig. 4 illustrates a preferred form of the blastant mixing valve.

"ted States Patent 0 "ice As will be understood more clearly by reference to Fig. 1, the invention comprises a blastant abrasive supply tank or chamber 10 of conventional construction, a mixing valve assembly 20, a servo mechanism 25, a supervisory control station 30, and a manually operative remote control device 40 carried by the blastant supply line 19 immediately adjacent to a directing nozzle or gun 60. The mixing valve assembly 20 includes a mixing chamber 12, a valve gateway or opening 13, a discharge chamber 14, and a control valve 11. The mixing chamber 12 includes means (not illustrated) communicating with the blastant supply chamber 10, from which chamber 12 is adapted to continuously receive blastant particles in a manner well known in the art. Supply line 18, which may be connected to any conventional source of fluid motive means, as for example, compressed air, communicates with chamber 12 and functions to cause the blastant particles to become mixed therein in a desired manner, and at the same time to carry such particles through the opening 13 into discharge chamber 14 and then through the flexible supply conduit or hose 19 to the directing nozzle 60 where the same will be blown out upon selected work articles. The supply conduit for the motive fluid may be connected with a separate source of the same; or with a motive fluid contained in chamber 10, analogous to existing blastant supply storage chambers, in a manner well known in the art.

The flow of blastant particles and motive fluid is adapted to be directly controlled by valve member 15 through operation of a servo mechanism 25, connected to its other end for this purpose. In the instant case, it is preferred to use a double-acting fluid motor comprising a piston member 16 connected to the valve stem 15, and which reciprocates in a chamber 17 under the r effect of fluid supplied to chamber 17 through a pair of control conduits 21 and 22 including valves 23 and 24, respectively. As will be apparent from an inspection of the figures, valve 23 controls upward or opening movement of piston 16 and valve 11, and valve 24 controls movement of piston 16 and valve 11 in its closing direction. Each valve is constructed as a conventional solenoid operated type and includes electrical wires 29 and 28, respectively, for causing energization of the same. Each valve also includes a fluid supply line, 27 and 26, respectively, which may be connected to any desired source of motor fluid, as for example, compressed air. In accordance with the present invention, valve 24 is normally biased to its open position and valve 23 to its closed position by suitable resilient means in a conventional manner, the responsive solenoids operating when energized to close valve 24 and open valve 23.

As will be apparent from the above description, the blastant supply valve 15 is normally adapted to be actuated to the closed position under the effect of the servo mechanism 25 when the respective control lines 28 and 29 for the solenoid valves are deenergized. When lines 28 and 29 become energized in a manner hereinafter specified, however, valve 24 will be closed and 23 will be opened to admit motor fluid to the lower end of chamber 17 to thereby cause piston 16 to move to its upper limit position and permit the blastant particles and propellent to egress from chamber 12 through conduit 14 to supply hose 19.

The lead wires 28 and 29 for the respective solenoid valves are in turn connected to a control station 30 in circuit with a light 32 and a pressure responsive switch mechanism 31. The particular circuit arrangement will be better understood from reference to Fig. 3 which shows valves 23 and 24 as being in parallel relationship with each other and with the pilot light 32 in a conventional A. C. circuit, L1., L-2. The pressure switch 31 is con nected in series with the line L-l, and as shown, is in its normally open position in which solenoid valves 23 and 2d and light 32 are all deenergized. However, when the contacts of the switch 31 are closed, both valves and the pilot light become energized to thereby cause valve 24 to close and valve 23 toopen, to in turn move piston 1-6 to its open limit position in which the mixing valve is in its upper position, or supply position.

Control station also includes means for connecting the pressure responsive switch member 31 with a pressurized line 33 and a remotely located pre sure control member 49. As shown in the figure, a con uit 35 (cou nected with a suitable source of ii id pressure, as for example, the same as that of conduit 3.3, or conduit 26 or 27) is connected in circuit with pressure chamber 37 through a manual control valve 3 3, a pressure reducing valve 35, a pressure relief valve 36, and pressure indicator 39. Pressure chamber 37 includes any aivcntioual type pressure responsive structure for actuating tie switch mechanism 31 in a manner well known in the art. The arrangement is such that the pressure of supply line 33 is reduced to a predetermined degree prior to its introduction into pressure chamber 3'? to permit the use oi a less rugged and less expensive pressure responsive switch device.

A flexible conduit or hose 38 also communicates with pressure chamber 37 and extends to the forward or nozzle end of the blastant hose 19 as shown where it terminates in a manually operative, remote control mechanism Hose 38 constitutes a mere extension of the pressure chamber 37 and terminates in a control valve at its extremity which regulates communication with atmosphere, and is adapted to control the pressure within pressure chamber 37 in a predetermined manner, i. e., to open and relieve the pressure or to close and permit the pressure to build up to a predetermined value. From the foregoing, it will beappal'ent that the control f the pres sure in line 33, and thereby pressure in chamber 31 from the manually operable, remote control mechanism 4t permits the switch mechanism 31 to exert supervision over servo mechanism 25 and therefore the flow of blastant from chamber 2-2 to supply hose 3?.

The details of the remote control mechanism 49 are more particularly shown .in Fig. 2 of the drawing and comprise a U-shaped guard or hand member which is fixedly but detachably connected about hose 19 by means of clamping strips 41 and 42, the clamping strips being secured to the guard member 45 as by means of pin members, 43 and 44 respectively.

The U-shaped guard member is perforated at one end thereof to form a passageway or seat 43 in which is threaded a valve nipple 59. Nipple 5t) includes a central conduit 51 and terminates within the confines of guard in an annular valve seat in which is positioned a dciorur able replaceable valve seating member as for a purpose hereinafter apparent. The other extremity of the valve nipple Si} is adapted to cooperate with the air hose 33 (indicated by dotted lines in the figure} and to form an airtight juncture therewith.

A spring 53 is positioned about the valve seat of nipple and is adapted to resiliently urge a pivoted lever member $5 in a counterclockwise direction (as viewed in the figure) about a fixed pivot 49 carried in a web 47 of the guard .ructure Lever 55 carries a conical pin member 5Z-Wl1iCh-l5 adapted to cooperate with the deformable seating member 56 in the nipple 5% to provide a closure valve for conduit 51 and hose 38.

Lever 55 includes an angularly related extension 57 having a terminal end which is received in a guide slot $6 in tic guard structure 45. The arrangement is such that spring 53 normally tends to move lever 55 to its valve opening position, as illustrated, in which the conical valve member 5?. is spaced from the seating ring 56 whereby luid pressure may escape from conduit 51, and accordingly hose 3-8, to reduce thepressure in the hose line and consequently-prevent energization of the pressure actuated switch member 31. Lever 55 is limited in its valve opening movement by abutment of the end of portion 57 against the cavity wall 46, as illustrated. Lever 55 also includes means for providing lost motion in its pivoting action, as shown by the clearance 54 provided between the lever and the pivot pin 49. This feature is exceedingly cfiective in preventing jamming, clogging and sticking of the lever under lengthy adverse operating conditions.

The valve closing movement of lever 55 in which the conical valve member 52' is seated against the deformable seating ring '56 is illustrated by dash lines B in the figure, to limit the position with which the valve can be seated against ring 56.

The operation of the device will be apparent from the preceding description but may be described briefly as depending upon the actuation or non-actuation of lever 55 when the operator grasps hose 19. In a blasting operation the operator will insert his hand through the guard 45 and over the lever extension '57, and the hose 19 be" tween the fingertips and thumb of such hand. This action forces extension 57 downward to the position indicated at E, wherein communication between conduit 51 and the atmosphere is cut off-by the seating of valve 52 in ring 56. This in turn permits pressure within line 38 and pressure chamber 37 to build up rapidly to the point where it is sutlicient to cause actuation of switch mechanism 31 and through the circuit L-1, L i, to close valve 24 and open valve 23. This in turn causes the servomotor 16, 17 to move to its upper limit position in which the main control valve 15 opens orifice 13 to permit the motive fluid from supply conduit 18 and the abrasive particles from the storage chamber 14 to be drawn into the mixing chamber 12 and through orifice 13 into outlet chamber 14 and thence through the supply hose 19 to the nozzle or gun 60.

The sequence-of control will be better understood from reference to Fig. 3 of the drawings which shows the control network in diagrammatical form. As illustrated, a series circuit, .L-l, L2, includes the pressure actuated switch mechanism 3-1 with a series contact switch member 31' in series with line L-l. The solenoid valves 23 and 24, as well as the signal 'light 32 are connected individually-across lines L-l and L-2 to provide a parallel work network. it will thus be apparent that with pressure actuator 31 in the raised or non-actuated position, the series circuit L-1 and L.'?. will be de-energized and therewith the solenoid actuated valves 23 and 24 and signal light 32. This condition permits valve 23 to remain in its normally fully closed limit position and valve 24 to remain in its normally fully open limit position to retain main valve .11 in the closed position. Actuation of pressure mechanism 31 through an increase in pressure in line 38 lowers the switch contacts 321 to complete the series circuit and energize both the solenoid actuated valves and the signal lamp, valve 23 moving to its fully open position and valve 24 moving to its fully closed position to actuate main valve 11 to the open position to permit the blastant mixture to move through T conduit 14 and line 19 to the discharge gun 60.

This operation will continue until such time as the operator relaxes or removes. his hand from within the guard 45, in which case the lever 55 is immediately urged to the upper limit position illustrated in Fig. 3, wherein air line 38 is opened to atmosphere via valve 56, 52. This permits the pressure in line 38 and pressure chamber 37 to drop below the value suilicient to retain switch 31 in itscircuit closing position, and the contacts of the same in circuit line L-l become separated. At this time, the solenoids of the respective control valves 23 and 24=beeome deenergi-zed-and the valves return to their respective opened and'closed positions under the effect of a conventional resilient thrust means, such as a return spring.

One of the significant and outstanding advantages of the present invention is the maintenance of a dependable operator responsive remote control device in combination with, and at, the directing nozzle of the blastant supply line in close proximity to the work, without encountering difficulties due to clogging or jamming of the working parts of such device through ricochetting blast particles and debris. This is because valve 52 is fully seated within ring 56 to completely seal conduit 51 and air line 38 at all times when the blastant stream is be ing fed through nozzle 60. It will thus be apparent that flying debris and blasted particles have very little chance to enter into or become trapped in the control valve mechanism.

Further, immediately upon the opening of valve 56, 52, a constant stream of pressurized fluid escapes from seating area 56 to continuously blow out any pulverized residue, grit or debris which may inadvertently have become lodged in or adjacent to the same. In this respect, the remote control mechanism is self-cleaning.

Another advantage resides in the inherent safety accorded the operator by the present control arrangement. Thus, should an operator become ill or injured and inadvertently lose his grip on the supply hose, lever 55 is immediately urged to its valve opening position by spring 53 whereby the pressure in line 38 and pressure chamber 37 drops off and switch mechanism 31 returns to its circuit opening position to control the servomotor 16, 17 and return valve 15 to its seating position in orifice 13 and shut off the blastant stream.

Still another advantage resides in the independent nature of the several components of the system in that the blastant supply structure, including chamber 10, valve mechanism 20, servo mechanism 25, and the remote control device 40 and nozzle 60, may all be located within a suitable sealed working enclosure while the control station 30 may be located outside the same. This positively precludes any danger of damaging such sensitive components as switch 31, meter 39, and valves 35 and 36 due to dust, grime, flying debris, etc. Further, the pilot light 32 provides an immediate indication of whether the apparatus is in operation or not and allows a simple, visual inspection by supervisory personnel to determine if the job is being accomplished without requiring entry to the working area.

Alternatively, the blastant supply structure, including chamber 10, valve 20 and servo mechanism 25, may be located at one central position, while the control station 30 is at a second position and the directing gun or nozzle 60 with the attached remote control device 40 is located within a working enclosure in a third position, all of which may be widely spaced from each other. This latter facility also simplifies supervision of a plurality of subordinate personnel engaged in a plurality of blasting operations at widely separated points from a single central ofiice, or the like.

It will be apparent to those skilled in the art that the present invention is not limited to the details of the embodiment described but may comprise other and different structures. As for example, remote control device 40 may directly control actuation of valve 15 through the pressure in such line, independently of the electrical control components described.

Although the present invention is not limited to any particular form of blastant supply structure, a preferred form of mixing valve arrangement which has been found to be exceedingly effective in practice is illustrated in Fig. 4 of the drawings. As shown, the valve 100 comprises a hollow, open-end cylindrical mixing chamber 101 connected at its lower end with a T conduit 102, the T member having a central vertical portway 110 communicating with the interior of the mixing chamber 101. The T member is substantially identical to that shown as chamber 14 in Fig. l of the drawings and need not be further described. The upper end of the mixing chamber includes an axial opening in which is positioned a valve stem guide member 103 having longitudinally extending tubular stern 104 projecting substantially midway within chamber 101. Valve stem guide 103 has a central aperture for guiding a valve stem 106. A stufling box 105 surrounds the valve stem and is adapted to seal the apertured stem guide in a well known manner. Stem 106 is threadedly connected at its lower end with an internally threaded valve head 107 which supports a valve disc 109 by means of a threaded stud 108. The arrangement is such that reciprocation of valve stem 106 within stem guide 103 will raise and lower valve disc 109 to respectively open and close communication between the interior of chamber 101 and portway 110. A compressed air connection 126 communicates with a passageway formed in the body of the stem guide and serves to equalize the pressure around stem 106 in order that dust and abrasive will not be carried along with the stem as it moves upwardly in the stem guide and the stuifing box. Any dust or abrasive leakage about stem 106 will eventually cause scoring and premature air leakage. The present arrangement greatly prolongs the useful life of the valve stem.

The mixing chamber also includes a lateral portway 111 which is adapted to communicate with an egress port in any conventional abrasive storage chamber, as for example, similar to that shown by the numeral 10 in Fig. 1. Portway 111 comprises a feed port through which the granulated abrasive material from the storage chamber may be selectively admitted to the mixing chamher 101. Communication between this portway and chamber 101 is selectively controlled by means of a slide or gate valve member 112 carried by a reciprocating gate guide 113. Guide 113 includes a lower cam projection 113' and an upper follower portion 114. The follower portion 114 engages the external surface of the valve stem guide extension 10 1 with a bearing support for stabilizing the valve gate 112 during its open and closing movements. The gate guide 113 extends laterally across chamber 1101 and terminates in an extension 115 which is adapted to be resiliently urged in a gate valve closing direction (i. e., downwardly to the fully closed position of valve 112 as illustrated) by a resilient thrust means 116. The extension 115 of the gate guide 113 forming a U- shaped or Scotch yoke type fit in connection with an end extension on a threaded stud member 123 to provide additional stabilization of the gate guide during its reciprocatory movement. It will further be apparent that the stud extension also serves as a limit stop for the gate guide 113 in its valve closing movement. The resilient thrust means 116 is preferably formed as a coil spring positioned about a guide stem 117 integrally extending from a guide plate 118 fixedly mounted in chamber 101 at the upper end thereof. If desired, the stud extension may be formed as an eccentric finger on the main stud body 123 in order that the limit stop position of the gate valve 112 may be varied at will.

Mixing chamber 101 also includes a second portway 121 diametrically opposite the abrasive portway 111. Portway 121 functions as a safety regulator, and for this purpose is covered by a removable closure cap member 122 which is normally securely anchored against portway 121 by a locking lever 124. As will be apparent from an inspection of the figure, locking lever 124 is pivotally connected at one end to the closure cap 122 and bears against the external surface of the mixing valve chamber 101 at the other end, the central portion of lever 123 being apertured to accommodate the same about stud 123. Lever 124 is located in its pre-set position by means of a wing nut 125 threadedly engaging the extended end of stud 123.

Upon assembly of the valve structure, the closure cap 122 is seated in portway 121 while lever 124 is simultaneously slipped over stud 123 with the upper end of the lever bearing against the external surface of chamber 101, the wing nut 125 thereafter being threaded on stud 123 to lock lever 124 and closure cap 122 firmly against portway 121. The arrangement is such that the blowofl" cap 122 may be easily removed from seating engagement over portway 121 by a simple manipulation of wing nut 125. This permits the operator to clear the mixing chamber of pressure at anydesired time, as for example, after the main air supply has been shut OE and valve Jill has een closed in preparation for securing the equipment after working hours. It will further be appreciated that the blowofl cap also provides a ready means for inspecting and cleaning the interior of the mixing valve.

A further partway comprising an inlet port for the motive fluid used to carry the abrasive out of chamber 1:91 and T iii/TL is provided in the wall of chamber Hill at a point which is behind the valve stem extension 104 in the Fig. 4 illustration. This inlet port, if desired, may include suitable connecting structure for interchangeably but fixedly attaching a suitable conduit lead from a source of motive fluid, as for example, an air hose.

it is believed that the operation of the mixing valve will be obvious to those skilled in the art and will therefore be only briefly described. Spring lid normally retains the abrasive valve 112 in its shutoff or closed position when valve stem 1% seats disc 1% in portway 13rd. Thus when valv 199 is initially raised, as by energization of the servomotor 16, the outlet port lid is cracked open to permit a scavenging action by the motive fluid (compressed air) prior to any movement by gate valve Upon further upward movement by stem 1% and valve 199, the valve disc contacts the extension 1113' on the gate guide to open communication between the mixing chamber and the stored abrasive. Thereafter, the abrasive will be gravity t ed into chamber lid aided by the drag of the fluid stream through outlet port 119, and carried along with the stream to the discharge gun. When it is desired to shut oil the blastant supply, the servomotor is reversed and the stem 1% and valve N9 move downwardly. Because of the constant tension of spring M6, the gate valve 12 always seats first, closing Oil the abrasive supply and permitting the motive fluid to scavenge the mixing chamber and outlet portway. This operation precludes clogging and sticking and has materially increased the useful. life of the mixing valve.

ts many apparently widely diflerent embodiments of this invention may be made without departing from the spirit and scope hereof, it is to be understood that this invention is not limited, except as defined in the appended claims.

What is claimed is:

l. in an abrasive blasting system including a source of abrasive material under pressure, a blastant nozzle connected to said source oi abrasive material, a fluid-pressure actuated supply valve mechanism interposed between said source of rasive material and said nozzle, said valve not lily closing communication between said source of abrasive material and said nozzle, a conduit having one end positioned adjacent said nozzle and having its opposite end connected to an electrical switch, said electrical switch being normally maintained in its open position and being adapted to be closed by fluid pressure, said switch being provided in an electrical circuit for operating a pair of solenoid valves, one of said solenoid valves being normally open and the other of said solenoid valves being normally closed when said switch is in its open position, and being movable to their opposite positions when said switch is in its closed position, said solenoid'valves being in fluid connection with said supply valve to maintain said supply valve in its normally closed position when said switch is open and to open said supply valve when said switch is closed, a control valve positioned adiacent said nozzle and adapted, when closed, to effect an increase of fluid pressure on said switch, means biasing said control valve to its open position, and manually operative means for closing said control valve.

2. In an abrasive blasting apparatus including an abrasive supply source having abrasive material under pressure, a blasting nozzle connected to said abrasive supply source through aIfluid-actuated supply valve mechanism, said supply valve mechanism comprising a housing, a valve seat, a piston having a valve head movable toward and away from said valve seat, means on said piston opcrativeto move said valve head toward and away from said valve seat under the influence of fluid pressure, said means comprising a flange on said piston, said flange being positioned in a fluid pressure chamber, means for applying fluid pressure in said chamber on opposite sides of said flange, electrical control means for applying fluid pressure on a predetermined one of said opposite sides oi said flange in accordance with the position of a fluid pressure operated electrical switch electrically connected to said electrical control means, said switch being con nected to a diaphragm which acts to open said switch when one side of said diaphragm is exposed to atmosphere and to close said switch when said one side of said diaphragm is shut oil from atmosphere, and a triggeroperated control valve means adjacent said nozzle and in fluid connection with said diaphragm, said control valve means being adapted to expose said one side of said diaphragm to atmosphere when said control valve means is open and to shut said oneside of the diaphragm oil from atmosphere when said control valve means is closed, said control valve means being biased toward the openposition but being adapted to be closed when pressure is applied to the trigger which is connected thereto.

3. Theabrasive blasting apparatus of claim 2 wherein said blasting nozzle is connected to said abrasive supply source through a flexible conduit, and wherein said trigger-operated control valve is in fluid connection with said diaphragm by means of a separate flexible conduit.

4. The abrasive blasting apparatus of claim 2 wherein said means for applying fluid pressure on a predetermined one ofsaid opposite sides of said flange comprise a pair of solenoid operated valves,=one of said solenoid operated valves being in fluid connection with said chamber on one'side of said flange and the other of said solenoid operated valves being in fluid connection with said chamber on the opposite side of said flange, one of said solenoid operated valves being open and the other being closed when said switch is open, and said one of said solenoid operated valves being closed and said other being open when said switch is closed.

5.1m an abrasive blasting system, a supply-housing connected to a source of abrasive material under pressure, a supply-chamber connected to said housing by means of a supply-passage, a fluid-pressure actuated supply-valve in operative relation to said supply-passage toclose said passage when fluid-pressure is applied to said supply-valve from one'direction and to open said passage when fluid-pressure is applied to said supply-valve from a second direction, a fluid-pressure source for supplying fluid under pressure to actuate said supply-valve, controlvalve meansconnec'ted bet-ween said fluid-pressure source and said supply-valve, solenoid means operatively connected to said control-valve means, said control-valve means selectively applying fluidpressure, in either of said directions, to said supply-valve upon selective operation of said solenoid means, said solenoid means being electrically connected to a fluid-pressure-operated switch, said switchbeing operatively connected to a trigger mechanism, which is positioned adjacent a nozzle, by means of a fluid conduit having an open end adjacent said nozzle, said open end being normally open to atmosphere and said nozzle being in fluid-connection with said supply-chamber, said trigger mechanism including a cut-off valve con structed and arranged to close the open end of said fluid conduit off from atmosphere when a predetermined pressure is applied against said trigger mechanism, said cutoff valve being resiliently biased into its open position, wherein it is spaced from the open end of said conduit, when said predetermined pressure is removed from said trigger mechanism, said switch being open to deencrgize 9 said solenoid means, and to, thereby, prevent operation of the system, when said cut-off valve is in its open position, and said switch being closed to energize said solenoid means, and to, thereby, actuate the system, when said cut-off valve is in its closed position.

References Cited in the file of this patent UNITED STATES PATENTS 1,641,342 Mauney et a1 Sept. 6, 1927 10 10 Wolever Aug. 6, Johnson Dec. 14, Campbell Apr. 16, Bick Nov. 13, Myers M Feb. 26, Mead Dec. 7, Ray Aug. 2, Buttolph Oct. 2, Sedgwick Apr. 7, 

